1. Field of the Invention
The present invention relates to plasma etching. In particular, the present invention relates to a method for plasma etching vias in printed circuit boards.
2. Description of Related Art
Modern printed circuit boards include multiple layers of circuits separated by insulating layers of dielectric material. Such printed circuit boards further include vias or contacts that interconnect circuits that are disposed on different layers. In situations wherein other electrical components are attached to the printed circuit board, contacts of the electronic components extend into the vias and are electrically connected to the desired circuits on various layers of the printed circuit board.
During the manufacture of a printed circuit board, vias are typically formed in the printed circuit board by a drilling process. During the drilling process, dielectric material from the insulating layers is smeared onto the electrically conductive material of the circuits. Prior to insertion of electronic components, the smeared dielectric material must be removed or “de-smeared” from the circuit material. Moreover, it is desirable to “etch back” or remove a small amount of the insulating, dielectric material immediately adjacent the via to improve the electrical connection between the electronic component and the circuits of the printed circuit board.
Radio frequency-driven, low-power plasma etching is often used to de-smear and/or etch back vias in printed circuit boards. Typically oxygen, nitrogen, and tetrafluoromethane are combined and used during the plasma etching process to de-smear and etch back printed circuit boards. Conventional plasma etching processes, however, fail to provide uniform etching through the via, resulting in quality issues. Moreover, the amount of etching varies between vias, specifically between vias of different diameters. Thus, the operating parameters must be adjusted depending upon the size of the vias in a particular printed circuit board. Also, it is conventionally recognized that higher levels of tetrafluoromethane result in higher etching rates. Higher amounts of tetrafluoromethane, however, increase the operating costs of conventional plasma etching processes.
There are many plasma etching processes well known in the art, however, considerable shortcomings remain.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.